1. Field of the Invention
The present invention relates to an optical attenuator including a magneto-optic crystal.
When conducting experiments with or adjustments of an optical communication system, sometimes an optical attenuator is used for adjusting the intensity level of an optical input to any device which is part of the system. As an optical attenuator, one adapted to mechanically vary its attenuation factor is known. However, in the case where an optical attenuator is incorporated in a system with the attenuation factor thereof being one of the objects to be controlled, it is desired that an optical attenuator having no mechanically moving part be put to practical use to improve reliability on the system.
2. Description of the Related Art
As optical attenuators which have so far been in practical use, there is one in which the attenuation factor is changed by a mechanical motion. For example, having an attenuation film with a varying attenuation factor distributed thereon inserted in the optical path, the attenuation factor of the optical attenuator can be adjusted by shifting the attenuation film.
However, it sometimes becomes necessary in practice to use such an optical attenuator incorporated in a control system in which the attenuation factor of the very optical attenuator is an object to be controlled. An example is a case where, in an optical amplifier adapted to amplify a signal light wave by conducting the signal light wave together with an pumping light wave through an optical fiber doped with a rare earth element such as Er (erbium), the power of the signal light and/or pumping light is controlled in accordance with the monitored level to thereby obtain a required characteristic (for example S/N ratio). In such a case, use of an optical attenuator adjusting the attenuation factor mechanically should be avoided in order to secure reliability on the control system.
Accordingly, an object of the present invention is to provide an optical attenuator having no mechanically moving part.
Other objects of the present invention will become apparent from the following description.